Tristans Twisted World: Mass Effect 3 Destroy ending

Destroy is the choice that they wanted you to make but in the end there are other ideas tossed in. Shepard cant stay the course but all Machines will also be destroyed. Its risky but from a personal standpoint I set out to destroy them and thats what I was gonna do. The future is simple as they can rebuild even the Geth and EDI but will they do that is a question and why is Shepard alive on earth in the highest possible ending?